In this page : http://fallout.fandom.com/wiki/Fallout_3_armor_and_clothing#Power_armor
There's a second value in parenthesis in some of the power armors' weight, like in brotherhood and enclave power armor, anybody knows what that value is?
It doesn't match up exactly, but my best guess is that it might be the adjusted weight of the armor after the +1 or +2 Strength bonus applied after equipping the armor. Each point of Strength boosts your carrying capacity by 10lbs, so an armor with +1 strength weighs 45lbs in your inventory but raises your overall carrying capacity by 10lb if worn. In effect, the armor would only weigh 35lbs because the stat boost negates some of the weight.
Keep in mind though, SPECIAL cannot be raised beyond 10. If your character has a Strength of 9 (and its a +2 bonus) or 10, the bonus carry weight will not applied, so you will carry the full weight of the armor. XxSick DemonxX (talk) 08:23, July 26, 2015 (UTC)